Good advice given. Even though it is a ranch hunt, I would really work on conditioning before you go. The elevation can really get you if you don't watch out. I do a combination of power walking with a backpack and bike riding (real or stationary). Jogging is great if you can do it, but my knees and back can't take that any more. Even so, it takes 2-3 days to get used to the altitude, so it is better to get there early if possible. Don't drink alcohol or caffeine for the first few days either, can make altitude problems worse. Plain old rolaids and ibuprophen will help also, I usually get headaches for a couple of days. Vitamin C really helps with sore muscles, but you have to take up to 3 grams 3 times daily.

Now for the clothes. You need a really good pair of longjohns. Regardless of cold, when you hike in the mountains, you will sweat. Long johns need to trasfer this moisture to outer layers or when you stop, or you will get cold. Think wicking ability, not actual warmth as the purpose of longjohns. If you go with some cotton longjohns, you will freeze.

Take 2 pairs of boots, both broke in: one without insulation and one with insulation. Get thin polypropylene sock liners to wear under wool socks. Liners wick moisture and keep the blisters down.

Also have a good pair of breathable raingear. I have a set of Cabelas uninsulated packable raingear with a goretex type breathable material. That way you can layer for warmth and just put on the raingear over that, or if it is warm, just use the raingear without warm clothes underneath.

Good luck.